1. Field of the Invention
The present invention relates to a system for coating or covering weld joints in a pipeline. More particularly, the present invention relates to an assembly and process for applying and heating a sheet of heat-shrinkable material which is wrapped around a pipe to form a sleeve used to cover the weld joints in a pipeline.
2. Prior Art
Various methods and systems are used to cover the weld joints of a pipeline which has been made up from pipe sections welded together in end-to-end relation. These pipe sections have been previously coated at the mill, except for the ends, which as indicated above, are welded together in the field. The pipe joints are then protected from corrosion by coating them in the field with an epoxy material, or with a polyethylene material, or by covering these weld joints with asphalt sleeves or heat-shrinkable polyethylene sleeves.
The heat-shrinkable sleeves (sometimes referred to as "shrink sleeves") are generally formed from sheets of heat-shrinkable material which are pre-cut to the desired pipe diameter for forming a sleeve and to provide for a manufacturer's suggested overlap. The sheets of heat-shrinkable material (generally provided in the form of rolls) comprise an outer polyethylene side and an inner mastic side which goes against the pipe. The current method of applying shrinkable sleeves to a pipe weld joint includes the steps of cleaning the weld joint and then manually wrapping the pre-cut sheet (or tape, as it is sometimes called) around the pipe over the weld joint so that the ends overlap approximately six inches; then, a non-shrinkable patch is tacked over the sleeve ends by heating it with a blow torch; next, the weld joint is heated with the blow torch and the sleeve is centered over the weld joint; next, the above blow torch is used to heat the sleeve until shrinking is completed; and finally, a small hand roller is run over the sleeve area to push out any trapped air.
Searches were conducted on the present invention and the following patents represent the results of the searches:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,637,199 Streck et al January 26, 1987 4,595,607 Betteridge et al June 17, 1986 4,502,905 Jung et al March 5, 1985 4,261,785 Hunter April 14, 1981 4,533,419 Pieslak et al. Aug. 6, 1985 4,113,545 Stuart Jr. et al. Sept. 12, 1978 3,697,354 Brown et al October 10, 1972 3,547,731 Stuart Jr. et al. Dec. 15, 1970 3,470,057 Stuart Jr. et al. Sept. 30, 1969 4,322,262 Cottam March 30, 1982 3,994,766 Dedels Nov. 30, 1976 3,426,118 Chapman et al. Nov. 17, 1964 3,499,817 Haven et al. March 10, 1970 3,776,803 Kissell Dec. 4, 1973 ______________________________________
The Betteridge et al patent is similar only with respect to the use of a rotating ring to induction heat the pipe. The present application differs mechanically by the use of a roller together with means to guide a pre-cut length of heat-shrinkable material onto the pipe, and an external radiant heater to set a closure patch. The present application also differs in that applicants are applying a completely different material by a different procedure and apparatus.
A pipe wrapping machine having a circumferential yoke that engages a section of pipe is disclosed in U.S. Pat. No. 3,470,057 to Stuart Jr. et al. The Stuart machine comprises a frame which is manually rotated about the pipe as it wraps a protective strip of material over a pipe joint in a helical manner. The above apparatus has an overhead gas heating chamber by which the adhesive side of the material is fed across the chamber to provide direct contact to melt the adhesive immediately prior to application to the pipe. Although the Stuart, Jr. patent is intended to wrap a short length of pipe (e.g. a weld area), it is designed to spiral wrap, not to wrap and provide a method to join the overlapping ends of the wrap. Further, the means of heating employed by Stuart is of no use for the purposes of the present invention. The heat-shrinkable tape employed in the present application is a two-layer product consisting of an internal low-melt mastic and an external higher-temperature shrinkable material,
If one were to attempt to use the teachings of Stuart et al to apply the heat-shrinkable tape employed in the present invention, one of two undesirable results would occur: (1) If the operator successfully melted the mastic, it would deposit on the heater itself, and either cool between heater and pipe, or cool upon contact with the pipe (allowing no flow). (2) If the operator were able to bring the sheet or tape (outer layer) to shrink temperature, the mastic would run off the sheet, the sheet would shrink prematurely, and since it has little capacity to retain latent heat, would stop shrinking between heater and pipe, and would certainly stop shrinking upon contact with the cold pipe. (It should be remembered that proper or full shrinkage requires maintaining temperature over a period of time--maybe 30 seconds.)
A similar portable joint wrapping machine is disclosed in U.S. Pat. No. 3,547,731 to Stuart Jr. et al. The variation in this apparatus of Stuart's includes a bowed roller for compensation of the differences in pipe diameters. The adhesive of the wrapping material is melted by direct application of the flame of a handheld propane torch.
A third circumferentially engagable pipe wrapping machine is disclosed in U.S. Pat. No. 4,113,545 to Stuart Jr. et al. This apparatus comprises another manually operated frame for the application of a cold wrap coating material.
In U.S. Pat. No. 3,994,766 to Dedels, a very large pipe cleaning and wrapping machine is disclosed. The Dedels device includes a superstructure disposed about the pipe and an adjacent tracked vehicle. The patent to Dedels is typical of over-the-ditch wrapping machines which are designed to clean and wrap cold-applied tapes on a continuous run. This patent is relevant only in showing that taping pipes is a standard practice.
U.S. Pat. No. 4,261,785 to Hunter is similar to Dedels, discussed above, in that it is typical of over-the-ditch wrapping machines which are designed to clean and wrap cold-applied tapes on a continuous run. In addition, this patent shows a conventional ring gear means for rotating a fixture.
U.S. Pat. No. 4,533,419 to Pieslak et al. discloses the standard method for the application of a patch closure using a blow torch.
U.S. Pat. No. 3,776,803 to Kissell is pertinent in that it applies a heat shrinkable material in the form of a sleeve to a duct. The sleeve is preformed, and as such, must be slid over the pipe. This precludes its use for pipeline application. Secondly, the whole apparatus is designed to rotate the pipe. Thirdly, all heat is externally applied, which would result on poor flow of mastic, especially without a roller. However, Kissell does discuss some of the well known characteristics of heat-shrinkable films.
U.S. Pat. No. 4,502,905 to Jung et al shows a conventional ring gear means for rotating a fixture.
U.S. Pat. No. 3,697,354 to Brown et al shows a pneumatic biasing means for a stay fusing machine.
U.S. Pat. No. 4,637,199 shows an eliptical coil in a machine for sealing paperboard packaging material.
No prior art device discloses a relatively compact motor driven machine for the application of a heat-shrinkable sleeve that can be readily operated by two persons. No prior art machine discloses a single system comprising both induction and radiant heat for the purpose of preheating the pipe prior to the application of the heat-shrinkable material which forms the sleeve. No prior art apparatus provides a single device and process for first the application of the heat-shrinkable material in the form of a sleeve and then the shrinking of the sleeve by heating in accordance with manufacturer's specifications.
The state of the art in heat-shrinkable sleeve application for girth welds is two men with torches. The present machine improves the uniformity, repeatability and quality of the coating, while increasing the speed and eliminating a man. Although some of the prior art patents might have some general similarities with respect to specific sub-components of the overall machine, these prior art machines are not capable of, or designed to, handle the product.